Due to their widely ranging mechanical properties and their ability to be relatively easily machined and formed, polyurethane foams have found wide use in a multitude of industrial and consumer applications. In particular, polyurethane foams have been found to be well suited for many applications. Automobiles, for instance, contain a number of components, such as seat cushions and vehicle interior components, such as headrests, that include polyurethane foams. Such polyurethane foams are typically categorized as flexible, semi-rigid, or rigid foams with flexible foams generally being softer, more pliable, and more subject to structural rebound subsequent to loading than rigid foams.
Polyurethanes are formed when isocyanate (NCO) groups (or A-side reactants) react with hydroxyl (OH) and other active hydrogen groups (or B-side reactants). Specifically, a carbamate linkage (or urethane bond) is formed upon the reaction between an isocyanate group and a hydroxyl group. The polyurethane polymer-forming reaction occurs between substances with more than one isocyanate group per molecule (or A-side reactants) and substances with more than one hydroxyl or other active hydrogen group per molecule (B-side reactants). The most common method of polyurethane production is via the reaction of a polyol (a B-side reactant) and an isocyanate (an A-side reactant) which forms the backbone urethane group. A cross-linking agent may also be added. Depending on the desired qualities of the final polyurethane product, the precise formulation may be varied. Variables in the formulation include the type and amounts of each of the reactants.
“Compression set” is the permanent deformation that takes place in foam after being compressed for an extended period of time. Polyurethane foams used in the automotive industry are exposed to significant stresses during normal use. Undesirable compression set can adversely affect appearance and performance of foam components. As such, lower values of compression set are desirable. Most foam customers specify the conditions for the testing for compression set and also have maximum levels allowed for compression set. These are some of the more challenging specifications to meet and they are becoming more so as efforts are made to use naturally-sourced materials and non-fugitive catalysts.
Thus, there is a need to provide a high quality polyurethane product having acceptable compression set while minimizing environmental impact.